It is known to provide a blocking liquid in a shaft seal to assist in the sealing action between the gas space and the atmosphere of relatively rotating sealing members.
The blocking-liquid sealing arrangement of the prior art, over which the present invention constitutes an improvement, operates with a floating ring seal. Floating ring seals are radial gap seals with play between the rotating shaft and the sealing ring connected with the seal housing and radially movable therein.
The purpose of the blocking-liquid sealing arrangement is to support the sealing action by providing a liquid pressure which is greater than the gas pressure against which the seal is provided. The pressure difference is generally small in the conventional units, for the most part about 0.5 bar. This pressure differential is small to keep the internal leakage quantities at the gas-side sealing ring as small as possible. The radial gap at the outer sealing ring is so dimensioned that the rate of flow of the blocking liquid can constitute a coolant stream capable of providing the requisite cooling of the gas-side sealing ring. The volume rate of flow of the coolant stream is generally proportional to the sealing pressure.
That means that an optimum cooling can only be provided for a given pressure range and that the turbocompressor must be limited in versatility to operate in this range. Stated otherwise, for a turbocompressor in which the blocking liquid forms the coolant and the flow of the coolant is determined by the radial gap in the outer sealing ring, the operating pressure range of the turbocompressor must be limited.
In addition, at high pressures, the control of the pressure difference between the blocking liquid on the one hand and the gas space to be sealed on the other is difficult, because the pressure difference, by comparison to the gas pressure to be sealed, is very small.
The control is effected by an applied pressure regulation and an indirect pressure difference regulation by control of the liquid level of the blocking liquid in a reservoir therefor. The generated pressure difference is proportional to the geodetic height of the blocking liquid in this reservoir relative to the shaft of the turbocompressor.
The blocking liquid is brought to an elevated pressure by the high-pressure pump and is depressurized in the radial gap of the outer floating ring to atmospheric pressure. The amount of the blocking-liquid source in the elevated reservoir must be sufficient to provide a controlled action of the seal upon failure of the blocking-liquid supply. Upon standstill of the turbocompressor under pressure, the blocking-liquid system must be maintained in operation to maintain the seal. Since the blocking-liquid system is an open system, the cost of operation is substantial.